Electron discharge device



W. W. WATROUS, JR

ELEGTRONK`DISGHARGE DEVICE Aug, 7, 1945.

Filed Sept. 24

ATTORNEY .m1 mw 1W w M Patented` Aug.I 7, 1945 gasten ELECTRON DISCHARGE DEVICE Ward W. Watrous,v `J r., Chatham, N. J., assgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 24, 1943, Serial No. 503,598

(Cl. Z50-27.5)

i4 claims.

This invention relates to electron discharge devices of electronic characterization, and more especially such devices of the general nature of arc rectiers, particularly thyratrons. v

The usual attributes of a thyratron are the provision of a cathode, grid, anode and small amount of vapor or inert gas by virtue of which a current passes through the device as an arc, starting whereof is controlled by the grid but wherein the grid exercises no further control after the arc starts either to modulate, limit or extinguish the arc. The arc, however, is stopped periodically by reversal of the anode voltage. The cycle of starting and stopping repeats at a rate dependent on the supply frequency so the tube operates with an intermittent arc discharge and is capable of controlling large currents. Emission from the grid is detrimental in use because of its effect in prematurely starting the discharge; and fundamentally an object of the present invention is to overcome undesirable grid emission and premature starting or loss of control.

Inasmuch as grid emission is aggravated when the grid is hot, a further basic object of the invention is to provide adequate heat-dissipation from the grid to maintain and operate the grid at as low a temperature as possible.

It is also a most serious eilect inherent in thyratrons heretofore employed that the grid when hot may cause ionization Within the tube at a time when the-anode is negative with respect to the cathode, thus encouraging arc back, and it is a desideratum of the present invention to overcome the causev of that undesirable condition.

Further objects of the invention are to provide for rigid support for the grid; to readily obtain and maintain proper alignment; provide for lead-in thereto from the press and stem rather than from the envelope wall; to provide for adequate thermal and electrostatic shielding and control of the electron flow and onset of ionization; and to simplify the construction and manufacturing operations.

Still furtherA objects will appear as the description progresses, both by direct recitation lthereof and by implication from the context. Vvv Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;

Figure 1 is a sectional elevation of an electron discharge device embodying my invention:

Figure 2 is a similar view of a portion of the showing of Fig. 1 in section, as on line II--II of Fig. 3, but on larger scale; and v Figure 3 is a cross-sectional view on line III-III of Fig. 1.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral I0 designates a glass or other suitable envelope of an electron discharge device which is evacuated and provided with a small quantity of ionizable inert gas, such as mercury vapor, helium, neon, argon, Xenon and the like. The envelope is provided with a reentrant stem II through which lead wires are sealed for making connection with exterior terminal prongs I2 on the bottom of an attached base I3. The opposite end of the envelope has its opposite or upper end constricted, as at I4, and capped thereab'ove with a terminal I5 which, makes connection with a depending rod I6 sealed through the glass at the upper part of the dome, toaxial therewith, by an upper stem I'I. The lower end of the depending rod I6 carries in the present showing, a transverse coaxial electrode constituting the anode I8 for the thyratron.

Opposed to the anode, and suitably supported by lead-in wire 20 from the main stem at the base end of the envelope, is a cathode 2| of appropriate construction and electron emissive under influence of a suitable heater. Between the cathode and anode is a control grid 22, the construction whereof is of especial concern to the present invention. It should be called to attention at this stage, that the control characteristic of a thyratron grid is governed by the dimensions of the opening therethrough. 'I'he present showing of control grid 22 accordingly provides a single circular opening 23 for passage of electrons, said opening being coaxial to the axis of cathode and anode. As shown, the grid includes a generally flat and ring-shaped plate 22' with a flange 24 at its inner periphery and another flange 25 at its outer periphery, both flanges being shown projecting downwardly from the ilat portion of the said grid plate. The inner flange 24 denes the grid opening 23 and constitutes the portion of the grid having direct effect on the electron flow. The area of the grid longitudinal of the tube and represented by the interior surface of inner ange 24, is kept at a minimum, and by virtue thereof the area of grid directly exposed to theV heat emitted from the cathode and from the arc stream is small. This results in the absorption of a minimum amount of heat by the grid.

This factor not only reduces the temperature but also the grid power requirements of the grid signal source which is important in the case of low impedance grid circuits.

The control grid 22 is preferably fabricated from a material of high heatl conductivity, high thermal emissivity, reasonably high melting point, and a surface which has a poisoning effect on vaporized emission coating lodging thereon, examples of such surfaces being carbonized nickel, graphite, or oxidized tungsten and chromium. The construction as indicated in the drawing likewise enables the grid plate 22 to be made of relatively thick material which increases the rate of heat flow transversely to the outer periphery of the control grid.

'I'he outer periphery of the control grid 22 consists of a radiator 2B, here shown as a metallic cylinder with the grid plate 22 therein approximately midway of the length of the cylinder and transverse thereto. Outer flange 25 on the grid plate enables the grid plate and radiator to be secured together with a close lit and by welding. The radiator is exposed to the envelope wall so that heat transmitted to the radiator from the grid plate radiates readily to the exterior and is dissipated.

The characteristics of the control grid as specified above are important desideratums of my inproved thyratron. The high heat conductivity insures that the heat developed in the grid, by the heater energy and the arc energy, be conducted from the region near the grid opening as rapidly as possible. The high melting point of the material employed maintains the grid intact and avoids disintegrated particles from contaminating other contents of the envelope. The high thermal emissivity promotes the rapid dissipation of the heat developed by the cathode and discharge energy. Relative to the poisoning effect, it may be explained that it has been found that certain materials acting as bases for emissive coatings tend to minimize or reduce emission. Advantage is taken of this effect in fabrication of the present grid by using a material therefor, for instance selected from the examples above mentioned, which tends to prevent emission from the grid by emissive material lodging thereon.

The discharge is confined largely between the cathode and anode by a cylindrical shield grid, and a feature of the invention comprises appropriately supporting and spacing the control grid and shield without electrical contact and yet have the control grid both inside and outside the shield grid and both grids coaxial. Presence of the shield grid is desirable for accomplishing certain purposes, amongst which are; to obtain electrostatic shielding; to reduce quantity of emissive coating from the cathode depositing on the control grid and grid insulators; to reduce the quantity of heat radiated from the cathode, anode, and arc discharge and absorbed by the control grid, thus reducing temperature of the control grid; to provide an extra control element; and to minimize the amount of glass envelope exposed to the discharge. In explanation of these mentioned desideratums, it may be added that transient anode voltages in an unshielded tube may cause momentary shift of the grid bias characteristic and in extreme cases will cause loss of control. Provision of a shield grid overcomes this detrimental effect by reducing anode-control grid capacity which has the beneficial effect of reducing the magnitude of doughnut shape.

duced. The detrimental eect of emissive coating depositing on the grid has been discussed hereinbefore, such deposit making it possible for emission from the grid to occur. Grid emission is dependent upon temperature, so that increased temperature promotes the previously explained detrimental effects of grid emission. Thus the invention, by deterring the emissive deposit and by reducing emissive-actuating temperature of such deposit as does occur, provides a thyratron of greater reliability. The shield grid, in providing an extra control element in the tube, affords opportunity to apply a signal thereto, or a fixed voltage in order to shift the -control grid characteristic to the desired value. Lastly, the minimizing of the amount of glass envelope exposed to the discharge has its beneficial effect in overcoming instability caused by electrostatic charging of the bulb walls.

As shown, the shield grid is constructed in two parts, namely a lower cylindrical section 21 around the cathode and extending almost to the grid plate 22' of control grid 22, and an upper cylindrical section 28 extending from just above said grid plate to a position well above the anode, said sections being coaxial and of equal diameters one to the other. Each shield grid section has a transverse annular baille therein, the upper section having its baille 29 between yand parallel to the control grid plate and anode, whereas the lower section has its baffle 30 'between and parallel to the control grid plate and cathode. Each baille has an opening therethrough which in the present showing has been arbitrarily made corresponding in size and axial position to that of the control grid. While the control grid plate and shield grid baiiles are shown each with a single opening, the size, number and relation of openings may be varied in accordance with control desired, but ordinarily it is usual to have the openings of the bailles the same size as and coaxial with the corresponding opening or openings of the control grid plate.

The cylindrical shield grid sections are carried by a plurality of studs or supporting members 3| in turn carried by a collar 32 applied to the stem Il, general practice being to clamp the collar as tightly as possible without breaking the glass of the stem. The studs project upwardly from the collar at the outside of said shield grid sections 2'1, 28, and in contact with the surfaces thereof and are ultimately welded or otherwise secured thereon during assembly. The studs 3| preferably extend to the upper end of the upper shield grid section, but an upper end portion of each is left unwelded from said section, thereby enabling that end portion of the stud free to be bent outwardly. Said studs are of a suitably resilient metal and formed with the upper end portions normally in the bent-out or diverging position as above described. Closely adjacent to the upper ends of said bent-out portions are provided beads 32, one on each stud, and shown 'I'hese beads are of high electrical and thermal resistivity of which lava is illustrative. In the upper shield grid section and in registration with each bead is a slot 33 of appropriate size, shape and location to receive the portion of the bead projecting toward the shield grid section from the stud, so that an edge portion of the bead is held in the slot, 'and keeps the bead from sliding on the stud.

outer surface portion of each bead bears against the glass of the dome part of the envelope and `by virtue of the resilient pressure exerted by the studs, the assembly or studs and shield grid will be supported laterally and centered in the envelope. -1

Likewise on each stud is insulatlve means for rigidly mounting the control grid. Each said means comprises an inner sleeve 34 of ceramic insulating material, such as lava, or other steatites, which extends through a hole iitting the same in the grid plate 22'. On opposite end portions of the sleeve and engaging at facing ends against the grid plate, are insulator knobs 35 which preferably have their peripheral faces grooved, as at 38, for establishing a long surface path to deter current leakage longitudinally of the knobs. These knobs are received in notches 3l cut in the edges of the shield sections thereby enabling the maior portions of the shield section edges to be situated in closely spaced parallel relation to the flat portion of the grid plate. It will now be evident that the interpositioning of the insulator knobs between the shield grid sections and the control grid plate obtains a coaxial alignment and rigid support for said grid plate and holds it in parallelism to the contiguous edges of the shield grid sections and segregates the control grid electrically from the shield grid, but permits the control grid plate to extend through the shield grid and support the aforementioned radiator as an outermost part of the control grid assembly and in good heat-radiating position just inside the glass wall of the envelope.

Electrical connection for the control grid is obtained by attaching a wire 38 to the radiator and also to a lead-in wire 39 through the press and stem I l thereby completing circuit to the exterior through one of the terminal prongs I2 protruding from the base. By the rigid mounting oi the control grid plate above described there is no longer any need, as previously existed in thyratrons, to utilize the lead-in connection as a support for the grid, nor is it necessary, as taught .by the prior art, for instance in U. S. Patent 2,292,081 of August 4, 1942, to H. T. Maser, to utilize a side seal, difcult to manufacture, mechanically weak, and otherwise objectionable. The present structure likewise overcomes diiiiculty experienced with the patented structure of obtaining alignment of the control grid.

The construction of the present invention is one well adapted to production methods and to provide a thyratron of increased rigidity and permanence of physical and electrical characteristics and with electrode alignment readily obtained and positively maintained. Of utmost importance is the fact that energy received or transformed by the control grid in the form of heat is readily transmitted by the relatively thick and heat conductive material comprising the grid plate to the radiator exterior to all other parts in the envelope enabling the heat to be dissipated by radiation from the outer surface of the radiator exposed toward the exterior. With a copious radiation occurring through the wall of the envelope it will be apparent that the temperature of the control grid may be kept to very low values. The result is reduction in the amount of grid current and improved starting control for the power arc of the thyratron.

What claim is:

1. An electron discharge device comprising an envelope and opposed cathode and anode therein, a grid interposed between said cathode and anode, a radiator on said grid in proximity to the wall of said envelope, and a shield between said radiator and both said cathode and anode.

2. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, a grid transverse to and coaxial with said axis and interposed between said cathode and anode, a cylindrical radiator on said grid coaxial with said cathode, anode and grid and in proximity to the wall of said envelope, and a shield coaxial with and between said radiator and both said cathode and anode.

3. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, a grid plate transverse to and coaxial with said axis and interposed between said cathode and anode, a cylindrical radiator on said grid plate with part of the radiator above and part below said grid plate and coaxial-with said' cathode, anode and grid plate and in proximity to the wall of said envelope, and a divided shield -in part above and in part below said grid plate with one saidv part between the radiator and cathode and the other said part between the radiator and anode.

4. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, shielding means around the peripheries of said cathode and anode, and a grid interposed between said anode and cathode said grid projecting radially through said shielding means.

5. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, shielding means around the peripheries of said cathode and anode, and a grid of greater diameter than either said anode or cathode and interposed between said anode and cathode and projecting radially through said shielding means, and means for supporting said grid from said shielding means.

6. An electron discharge device comprising an 'envelope and opposed cathode and anode therein on a common axis, shielding means comprising longitudinal sections oi which one section is around the cathode and another section is around the anode, and a grid interposed between said cathode and anode said grid projecting between said sections of the shielding means.

7. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, shielding means comprising longitudinal sections of which one section is around the cathode and another section is around the anode, a grid interposed between said cathode and anode said grid projecting between said sections, and means for supporting said grid from said sections.

8. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, shielding means around the peripheries of said cathode and anode, a grid interposed between said anode and cathode and projecting radially through said shielding means, and a radiator on said grid outside of said shielding means.

9. An electron discharge device comprising an envelope and opposed cathode and anode therein on a. common axis, a shield grid around the peripheries of said cathode and anode. a control grid interposed `between said anode and cathode and projecting radially through said shield grid, and means for supporting said control grid from said shield grid, and a. radiator on said control grid outside of said shield grid.

10. An electron discharge device comprising an envelope and opposed cathode and anode therein on a common axis, a shield grid comprising longitudinal sections of which one section is around the cathode and another section is around the anode, a control grid interposed between said cathode and anode and between said shield grid sections, and a radiator on said control grid outside of said shield grid sections.

11. An electron discharge device comprising an envelope and opposed cathode and anode therein on a, common axis, a shield grid comprising longitudinal sections of which one section is around the cathode and another section is around the anode, a control grid interposed between said cathode and anode and between said shield grid sections, means for supporting said control grid from said shield grid sections, and a radiator on said control grid outside of said shield grid sections.

12. An electron discharge device having an envelope and electrodes of which one electrode is cylindrical and coaxial within the envelope, said cylindrical electrode being divided into two opposed sections, and another electrode transverse to said cylindrical electrode and projecting from between the said sections thereof, insulators interposed between said sections and said transverse electrode, and rods extending through said insulators and attached to both said sections.

13. An electron discharge device having an envelope and electrodes of which one electrode is cylindrical and coaxial within the envelope, said cylindrical electrode being divided transversely into two opposed cylindrical sections. and another electrode transverse to said cylindrical electrode and projecting from between the said sections thereof, insulators interposed between said sections and said transverse electrode, rods extend` ing through said insulators and attached to both' said sections, and heat dissipating means at the outer periphery of said transverse electrode outside oi and spaced from said cylindrical electrode and from said rods. 

